1. Field of the Invention
This invention relates to a sewing machine including mechanisms for driving a needle bar, a needle thread take-up, etc. respectively.
2. Description of Related Art
In conventional sewing machines, components are assembled into modules for driving a needle bar, a needle thread take-up, etc. The modules are sequentially mounted on a die-cast frame. Thus, a needle bar driving mechanism and a needle thread take-up mechanism are mounted on the frame as respective modules. Positions of the mechanisms need to be adjusted relative to a shuttle located below the mechanisms since the mechanisms are mounted on a frame of a sewing arm of the machine. These mechanisms need to be located close to each other and to have a predetermined positional relation to each other. Accordingly, the productivity of sewing machines would be improved when components required to perform a function are assembled into a single module and the positions of the components are adjusted in the module before the module is mounted on the frame.
In assembling components required to perform a function into a single module, desired positional relations among the components can easily be obtained when the components can be mounted on a common member. For example, a conventional sewing machine includes a sewing bed further including a left end which will be referred to as “head.” A part of the frame in the head may be separable from another part of the frame, and the components performing the respective above-described functions may be assembled onto the frame of the head. However, when the components are assembled onto the frame of the head, the weight of the head including these components is increased, and a junction between the frame of the head and another frame part is cantilevered to be rendered large-sized, whereupon the size of the sewing machine is increased. In view of the problem, it is suggested that the functional components be mounted on a plate-shaped member discrete from the frame without separation of the frame and the plate-shaped member be further mounted on the frame.
However, operations of the mechanisms and superimposition of the components cause load when the components of the needle bar driving and needle thread take-up mechanisms are mounted on the single plate-shaped member. Consequently, the plate-shaped member needs to have a high stiffness. Accordingly, since a mere plate-shaped member cannot support the components of the mechanisms, the components cannot be assembled into respective modules, whereupon the productivity of sewing machines is low.